1. Field of the Invention
This invention relates to a heat resisting alloy applicable to materials for high-temperature spring and wires for meshes of catalyzer for purifying exhaust gas in addition to materials for exhaust valves of various automobile engines and marine engines.
2 Description of the Prior Art
In recent years, the increase in the number of engine valves (for example, four valves per one cylinder) and the reduction in a diameter of the engine valve are promoted in order to obtain a high power and high rotational engine. Hitherto, high Mn austenitic heat resisting steel SUH 35 (Fe-9Mn-21Cr-4Ni-0.5C-0.4N) has been widely used as an exhaust valve material for gasoline engines, however as a high-strength exhaust valve material for high power engine used at 800.degree. C. or above, Ni-based super alloy NCF 751 (Ni-15.5Cr-0.9Nb-1.2A1-2.3Ti-7Fe-0.56C) are used.
The aforementioned Ni-based supper alloy is an alloy excellent not only in the high-temperature strength but also in the high-temperature oxidation resistance and the high-temperature corrosion resistance. Namely, although there is a problem of high-temperature corrosion caused by PbO and PbSO.sub.4 produced on a surface of the valve as combustion products in a case of using leaded gasoline which is added with tetraethyl lead in order to increase the octane value, the high-temperature corrosion resistance is improved in this super alloy by increasing the amount of Ni up to 70 wt %.
However, this super alloy contains a great amount of expensive Ni as much as 70 wt % and there is a problem in the cost, accordingly an alloy containing the Ni amount reduced down to 60 wt % so as to cut the price and yet having the property equal to that of the aforementioned super alloy of NCF has been developed (cf. Japanese Patent Application No. 63-95731/88).
Lately, removal or reduction of tetraethyl lead from leaded gasoline is forwarded and the problem concerning the high-temperature corrosion becomes not so severe as compared with before, therefore it becomes clear that alloys are available sufficiently for engine valve without improving the high-temperature corrosion resistance so much. However, a demand of reduction in price and conservation of resources becomes further strict in mobile application materials as compared before, and the demand from a viewpoint of the reduction in price and the conservation of resources is further increasing also in the exhaust valve materials.
Therefore, an approach for decreasing the Ni content has been carried out within a limit of exhibiting sufficient practical utility in the corrosion resistance since it has been known that corrosion loss caused by the aforementioned PbO attack is closely connected with the Ni content, and decreases along with an increase of the Ni content. For example, alloys for exhaust valves containing Ni of 40 wt % have been already disclosed in Japanese Patent Application No. 54-93719/79, No. 59-130628 and so on.
However, in the aforementioned alloys, there is a problem in that .eta.-phase (Ni.sub.3 Ti) which is a brittle phase is precipitated during the long time application at a high-temperature to reduce the high-temperature strength, therefore it is not possible necessarily to satisfy the aforementioned demand sufficiently.
Furthermore, the alloy are naturally required to be excellent not only in the corrosion resistance and the high-temperature strength, but also in the hot workability for manufacturing the engine valves and so on.